I'm not getting much sunlight. Especially now. But I was getting plenty when I lived in Dubai for several months. Didn't change anything much, my sleeping schedule was still slipping. So no, your theory is wrong.
Non-24-hour sleep/wake disorder is not something one can fix like this. I would if I could. I've had this problem since my late teens.
https://en.wikipedia.org/wiki/Non-24-hour_sleep%E2%80%93wake...